"Hypothetically, it is possible that such images are experienced so intensely because they imply biologically important situations; for example, potential physical danger or a potential mating opportunity, " adds Most, a postdoctoral fellow at Yale University.

Looking at photos

To determine what happens when we see emotional, graphic images, Most and his colleagues showed test subjects hundreds of photos in rapid sequence, using a computer program.

All of the photographs depicted landscape or architectural scenes, except for a few violent and gory images that were mixed into the sets that flashed by the viewers.

These photos showed things like a severed limb and a mysterious figure pointing a gun.

The study was repeated, only this time the researchers inserted erotic images into the sets. This test on eroticism is the focus of a separate, unpublished study.

Viewers for both tests were asked to look for certain photos showing the landscape or architectural scenes.

If these target images appeared directly after the gory or sexy photos, the viewers could not see them, even if the target images were turned sideways or if they received additional information about what they should be looking for.

You'll go blind doing that

The researchers discovered that viewers were blinded for one-fifth of a second after witnessing the eroticism or gore.

"Brain mechanisms that help us to attend to things become tied up by the provocative image, unable to orient to other stimuli," says Yale researcher Professor Marvin Chun, who also worked on the study.

"This is what causes the 'blindness'. Not real blindness, but functionally similar to being momentarily blind."

"This result is a striking example of how emotional reactions can influence what we consciously see. Although the practical ramifications of this sort of emotion blindness have not yet been tested empirically, it seems plausible that a variety of momentary 'blindnesses' like emotion blindness constrain what we see and don't see in our daily lives."

Different images, different effects

Dr Elizabeth Phelps, director of New York University's The Phelps Lab, whose members study cognitive neuroscience of memory and emotion, adds that some emotional reactions are subjective, so individuals could be blinded by different types of images.

David Zald, a Vanderbilt University psychologist who worked on the study, says there is an implication for advertisers.

"People in the advertisement industry have long known that erotic or disturbing images can grab consumers' attention," says Zald. "However, our findings suggest that if you present relevant information, such as a brand name, too quickly after an emotional image, the viewer might not actually process it.

"Thus, although a TV ad might be extremely successful at grabbing our attention, we may be left with absolutely no idea of what was actually being sold."